1. Field of the Invention
The present invention relates to electronic equipment including a first IC and a second IC which have communication capabilities to be actuated by different power supply systems, and to an improvement of a camera.
2. Description of the Related Art
FIG. 3 is a block diagram showing a major portion of the electrical configuration of a known camera. The components of the camera will be described below.
In the drawing, there is shown a main microcomputer (hereinafter an MCPU) 201 for controlling various operations of a camera. The MCPU 201 also controls power supply to a sub-microcomputer (hereinafter an SCPU) 202.
There is shown a lens control circuit 203 for controlling the focal position and aperture of a photography lens. While receiving a signal LCOM from the MCPU 201, the lens control circuit 203 carries out serial transmission over a data bus DBUS1, controls a motor according to the contents of the transmission, and controls the focal position and aperture of the photography lens. By contrast, the MCPU 201 receives focal position information of the photography lens, distance information, best focus correction information, and other various kinds of correction information from the lens control circuit 203.
There is shown a liquid-crystal display circuit 204 for displaying photographic information of the camera such as a shutter speed and aperture control value. While receiving a signal DPCOM from the MCPU 201, the liquid-crystal circuit 204 carries out serial transmission over the data bus DBUS1, and achieves liquid-crystal display according to the contents of the transmission. Also shown is a switch sensing circuit 205 to which, like the liquid-crystal display circuit 204, power is always supplied. In an ordinary camera, the switch sensing circuit 205 can always read the state of a switch SW1 interlocked with a first stroke to be made for starting a photography preparation movement of a release button of the camera, the state of a dialing member used to set a shutter speed in seconds, an aperture scale value, an exposure correction value, and the like, the state of a switch used to set an exposure mode, and the like.
Incidentally, power is supplied from a power source A, which is a first power line to the MCPU 201, lens control circuit 203, and liquid-crystal display circuit 204, respectively.
There are shown a photometry circuit 206 for measuring the luminance level of an object relative to each of a plurality of areas, into which a scene is divided, by performing through-the-lens (TTL) metering, and then sending measured luminance levels to the MCPU 201, a feeding circuit 207 for controlling a film feed motor according to a control signal sent from the MCPU 201 so as to wind up or rewind film, and a shutter control circuit 208 for controlling a shutter unit, which is not shown, according to a control signal sent from the MCPU 201. A release switch SW2 is interlocked with a second stroke to be made for starting a photographic (exposure) movement of the release button of the camera. When the switch SW2 is turned on, the MCPU 201 controls a shutter so as to start exposure.
There is shown a strobe light control circuit 209 for controlling strobe light and modulated light. The strobe light control circuit 209 is composed of a circuit for accumulating charge required for producing strobe light, a xenon tube serving as a flashing unit, a trigger circuit, a circuit for ceasing flashing, a photometry circuit for measuring light reflected from a film surface, an integrating circuit, and the like. When an X synchronizing (hereinafter sync) contact, which goes on with the run of a front curtain of the shutter, is turned on, flashing is started.
There is also shown a focus detecting circuit 210 for detecting focus according to a TTL phase-difference sensing method. The focus detecting circuit 210 is composed of a line sensor, an optical system driving mechanism, and a sensor drive circuit.
The sensor drive circuit starts accumulating charge in the sensor in response to a sensor charge accumulation start signal sent from the SCPU 202, completes accumulation of charge in the sensor when the charge accumulation level of the sensor becomes a certain level, and communicates completion of accumulation to the SCPU 202 over the data bus DBUS2 through serial transmission. The SCPU 202 in turn reads a sensor signal and communicates it to the drive circuit. This causes the sensor drive circuit to output a sensor driving signal to the line sensor. The SCPU 202 can, therefore, read a signal produced with the charge accumulated in the line sensor. The SCPU 202 then converts the read signal into a digital form synchronously with the sensor driving signal, and judges from the digitized image signal, according to a known phase-difference detecting method, whether or not the photography lens is focused on an object.
Incidentally, power is supplied from a power source B, which is a second power line, to the SCPU 202, strobe light control circuit 209, and focus detecting circuit 210, respectively.
Communication between the MCPU 201 and SCPU 202 is achieved through serial transmission over the data bus DBUS2 in such a way that the MCPU 201 first sends an MCOM signal, which is a communication request signal, to the SCPU 202.
There is shown a power circuit 211 for supplying power to the power sources A and B in proportion to the voltage of a cell. Power is always supplied to the power source A. However, power supply to the power source B is controlled according to a control (CTL) signal sent from the MCPU 201.
In known electronic equipment, such as a camera, having the foregoing components, a plurality of CPUs are used to control various operations of the equipment. In this kind of electronic equipment, power supply to the CPUs is often controlled in an effort to save energy. A communication line over which a group to which power is supplied from the power source A communicates with another group is the data bus DBUS1, and a communication line over which a group to which power is supplied from the power source B communicates with another group is the data bus DBUS2. Thus, a communication line is provided for each power supply system. By disconnecting the power source B, a high-level voltage is prevented from being applied to a terminal connected on the data bus DBUS2. Thus, current is prevented from flowing into the power source B.
However, when a communication line or signal line is provided for each power supply system, the following problems arise:
1) The number of pins of an IC employed must be large. This invites an increase in the size of the equipment. PA1 2) The circuitry including numerous special lines, such as communication lines, cannot be adapted to general-purpose equipment. This increases cost.